id Tech 2 is id Software's second fully-3D engine, first used in Quake II. The engine is based on a lot of the code from the Quake Engine (by many referred as id Tech 1.5) used in the original Quake.
The engine contained out-of-the box support for hardware rendering, mainly OpenGL, in addition to a software renderer. It used BSP for level environments with a static lightmap for lighting objects.
id Tech 2 has been open-sourced (something of a tradition with id Software which John Carmack insists upon), creating projects not only to enhance the original Quake II with modern graphics upgrades (such as Quake2Max and Quake II Evolved), but also projects by independent developers using the now-free engine such as Warsow.
This concept contains games that use the id Tech 2 engine; either the original or a slightly modified version.